1. Field of Invention
The present invention relates to the integration of electrical devices and connections in plastics, and in particular in components or structural parts which are made of non-conductive polymeric material and installed on-board a vehicle. More specifically, the invention relates to a method for the production of a component or a structural part on-board a vehicle that is adapted to integrate electrical devices and connections, and to a composite material for the realization of the component or structural part.
2. Description of the Related Art
In the automotive field, non-conductive polymeric materials are known in the art (for example, polyolefinic thermoplastic polymers which are commercially available as polypropylene (PP) or high-density polyethylene (HDPE)) for the realization of on-board components, including: fuel systems (tanks and other structural parts), internal finishing of the passenger compartment (dashboard, door panels), and external finishing of the vehicle body (bumpers, mouldings).
The on-board electrical or electronic devices which are installed in combination with these components (including sensors, devices for operating on-board systems, and devices for controlling the management of the functions in the passenger compartment) are typically made as discrete elements housed in seats obtained by moulding in the shape of the component. They are connected to remote power supply sources and to remote signal processing components by wiring laid along the chassis of the vehicle.
In order to avoid laying extensive lengths of wiring, different technological solutions have been developed for integrating the electrical connection lines in a plastic matrix, which forms a lining in the passenger compartment of a vehicle (or a structural component of the vehicle). A further development consists of the integration of the on-board electronic devices (for example, the devices for controlling the passenger compartment and bodywork functions) in the plastic components inside the passenger compartment (such as the dashboard and the door panels) where the devices may be embedded and touch-operated.
Published international patent WO 2007/096016 describes a lining for a vehicle in which regions, including switching, sensor, electrical, or electronic signal transmission functions, are formed. On-board functional devices, such as the sensor or control devices, are formed as discrete elements which are arranged in a mould for forming the lining prior to injection of the plastic, so as to surface at the side of the lining facing the passenger compartment, once moulding has been performed, and provide a touch-operation functionality. Flexible conductor strips are embedded in the plastic matrix during moulding for connecting the devices outside of the lining formed.
Published European patent EP 1,663,720 describes a touch-operated device that can be used on-board a vehicle and which includes a capacitive sensor arranged underneath a surface of an internal lining of the vehicle and which can be touch-operated by a person present inside the passenger compartment. Such a device may be integrated in the covering surface of an air-bag, inside a steering wheel, on a dashboard, within an armrest, in a control panel, or in any other surface of a vehicle which is suitable for interaction with on-board electronic devices.
Published German utility model DE 299 07 054 relates to an instrument dashboard, in particular for a motor vehicle, with a support made at least partially of plastic which includes display instruments and operating components that are powered by conductive tracks, in which the conductive tracks are made in electrically conductive plastic (for example, ULTRAFORM® produced by Basf or DURETHAN® and POCAN® produced by Bayer). The conductive tracks are preferably made in a flat form and combined with the support mechanically or chemically (for example, by an injection-moulding process).
Published international patent WO 2010/026000 describes a single-layer or multiple-layer lining for a vehicle, which has regions formed by a mixture of plastic and conductive material. The lining may be used as a part of the interior upholstery of a vehicle (for example, for dashboards or insides of doors). Predetermined areas are provided with conductive tracks for performing electrical conduction functions and more complex switching, sensor, or generally signal transmission functions, wherein the tracks are made of a mixture of plastic materials forming the lining and a conductive material (for example, carbon nanotubes).
A method for producing electrically conductive and/or piezo-resistive tracks on a non-conductive, composite, polymeric substrate including a matrix of commercially available polyolefinic thermoplastic polymers, with a dispersed-phase filler of carbonization promoters (such as carbon nanofibres or carbon nanotubes) is known from published international patent application WO 2012/055934, which teaches how to realize the conductive tracks by laser ablation and consequent localized pyrolysis of the substrate which results in the formation of carbonaceous conductive structures favoured by the promoters, which are able to participate in the conduction by concentration in the tracks.
However, although the aforementioned document suggests (in theory and in laboratory tests) using such a technology for the formation of electrical connections, and simple electrical devices (such as pushbuttons, sensors, antennas, etc.) are incorporated in polymeric substrates widely used in motor vehicles (such as polypropylene and polyethylene), it does not deal with the practical aspect of industrial application of this technology to the manufacture of the aforementioned elements in actual on-board components, nor the integration of the technology with the already established techniques for production of these components.
Components in the automotive field which benefit the most from integration with electrical devices (such as the dashboard or door panels) have particular forms which are determined by the ergonomic requirements associated with their use, or simply by their position in the passenger compartment. In such cases, their shaped forms are determined exclusively by the aesthetic appearance which the designer wishes to give to the passenger compartment of a vehicle, such that it may be distinguished from the design solutions of competitors. Moreover, the industrial technology of injection-moulding in the automotive field is nowadays optimized for the processing of polymeric compounds (which are commonly used for the production of these components), but the technology is not adapted to the processing of compounds with a dispersed-phase filler, the distribution of the filler affecting the electrical properties of the entire component and, even more specifically, the high electrical conductivity values which can be obtained by selective laser ablation of (bidimensional or tridimensional) regions of the component intended to integrate the designed electrical functions.
It is therefore desirable that the technology for the manufacturing of electrical devices and connections incorporated in non-conductive polymeric substrates should be improved for practical application thereof to specific on-board components of a vehicle and, vice versa, that the current technologies for moulding these components in the automotive field should be adapted to the new materials.
The main factors to be considered during the design of a motor-vehicle component using a polymeric material with a dispersed-phase filler having conductive properties which can be locally activated in a selective manner are strictly dependent on the suitability of the component to form conductive tracks with electrical conductivity properties which can be controlled depending on the desired design configurations. For this purpose, during the design of a component, the following parameters must be adjusted: the minimum distance between parallel conductive tracks, in order to prevent interference and short-circuits; the curvatures and plane variations of the conductive tracks, in order to avoid the formation of discontinuities therein; the geometrical configuration of the conductive tracks (length and cross-section) depending on the electrical characteristics of the signal, the polymeric material used and the foreseen electrical load; the geometrical configuration of the component made of polymeric material in the regions designed for an electrical device, in order to define controlled-deformation zones and realize control devices which can be activated by external deformation and pressure stimuli (based on the piezo-resistive effect of the conductive tracks); the geometrical configuration of the conductive tracks in the regions designed for an electrical device, in order to define capacitive proximity sensor zones and form control devices which can be operated by external touching actions, (based on the capacitive effect of the conductive tracks); and the technical solutions for connecting the component containing the conductive tracks to the on-board power supply and/or signal processing systems.